Where do floods happen? Floods happen in low lying areas. Floods would not happen in high places because all the rain would fall from a high place like a mountain. Here is a flood that happened in Calgary.
The sun heats the water on the ground such as puddles. The water evaporates in the air and becomes water vapour. Soon the water vapour condenses and forms a cloud. Eventually the water vapour will fall making it rain. If rain falls too fast then you could get a flood.